1. Field of the Invention
The present invention relates to a pen-shaped coordinate pointing device which indicates a position to be determined and an operation by an operator to a position detecting device, such as a tablet, for determining the position.
2. Description of the Related Art
Conventionally, a pointing device, called a xe2x80x9cpen and tabletxe2x80x9d, may be used as one of the input devices for computers. The pen and tablet is a combination of a platelike tablet and an input pen to be operated on the tablet by an operator. When the operator indicates an arbitrary position on the tablet with the input pen, the position is detected by the tablet and information about the position is output to a computer.
The assignee of this application has proposed various input pens and the like for pens and tablets, as disclosed in, for example, Japanese Examined Utility Model Application Publication No. 5-4034. An example of a conventional input pen will now be described with reference to FIG. 13.
FIG. 13 is a cross-sectional view showing the general structure of an input pen 90, as an example of a conventional input pen. Components of the input pen 90 are housed in a penholder 91, which has almost the same shape as that of a writing instrument, such as a ballpoint pen or a fountain pen.
At the leading end of the penholder 91, a lead 92 is disposed so as to be connected to the interior of the penholder 91. The base end of the lead 92 is positioned in a through hole formed in a ferrite core 94, and is fixed to a lead holder 96. The lead holder 96 is fixed to the penholder 91 via a spring 97.
The lead 92 has a ferrite chip 93. In a non-operation state of the input pen 90, approximately two-thirds of the ferrite chip 93 is positioned in the through hole of the ferrite core 94. The lead 92 is supported by the spring 97 together with the lead holder 96, so that it can move in the direction of expansion and contraction of the spring 97, that is, in the axial direction of the penholder 91, and along the through hole of the ferrite core 94.
The ferrite core 94 is cylindrical and has a through hole extending in the longitudinal direction, in which the lead 92 is inserted. A coil 95 is wound on the outer side face of the ferrite core 94, and is connected to a capacitor 98 in the penholder 91 so as to form a tuning circuit 99.
The tuning circuit 99 of the input pen 90 is excited in response to radio waves of a predetermined tuning frequency, for example, a frequency fo, output from a tablet (not shown), and induced voltage is induced in the coil 95. When the output of the waves is stopped, radio waves of a predetermined frequency are output from the coil 95 because of a current passing based on the induced voltage. The tablet receives the waves output from the tuning circuit 99, so that the position of the input pen 90 on the tablet can be detected.
The input pen 90 operates when the leading end of the penholder 91 is pressed against the tablet. During operation, the lead 92 is pushed into the penholder 91, and the ferrite chip 93 built in the lead 92 is moved toward the base end inside the ferrite core 94.
Because the coil 95 is wound on the ferrite core 94, as described, when the positional relationship among the ends of the ferrite core 94 and the ferrite chip 93 is changed, the inductance of the coil 95 is also changed. Therefore, in the tuning circuit 99 including the coil 95, the inductance of the coil 95 is changed by the movement of the ferrite chip 93, thereby changing the tuning frequency of the tuning circuit 99.
In this case, when a radio signal of a frequency fo is output from the tablet, the phase of the induced voltage produced in the coil 95 shifts from that in a non-operation state due to the change in tuning frequency of the tuning circuit 99. For this reason, the tuning circuit 99 outputs radio waves which are different in phase from the waves output from the tablet.
Accordingly, operation of the input pen 90 can be detected by exciting the tuning circuit 99 withradio waves output from the tablet and by detecting the phase difference between the waves and radio waves output from the tuning circuit 99.
As described in the above example, the conventional pen and tablet is easy to use because there is no need to connect the tablet and the input pen, and the operational feeling thereof is similar to that of typical writing instruments, such as fountain pens and ballpoint pens.
The conventional input pen, such as the above-described input pen 90, has a size similar to that of typical writing instruments, such as ballpoint pens, and is suited for use particularly in desktop computers and the like.
In recent years, size reduction of electronic devices has been achieved; for example, portable electronic devices, called xe2x80x9cPersonal Digital Assistants (PDA)xe2x80x9d have become widespread. For this reason, there has also been a demand for size reduction of input devices for use in small electronic devices. It is, however, difficult to achieve a substantial size reduction without changing the constructions of the conventional input pens.
As an example, the above-described input pen 90 must not only be shortened but must also be reduced in diameter for the purpose of size reduction. Therefore, the ferrite core 94 and the lead 92 must also be reduced in diameter.
Since the lead 92 has the ferrite chip 93 therein, however, if it is reduced in diameter, the wall surface of a portion thereof with the ferrite chip 93 therein also becomes thin. Since the lead and the like are made of resin in most cases, such thinning causes insufficient strength, and the lead 92 may undergo plastic deformation due to the load applied during operation. In a case in which the lead 92 is deformed inside the ferrite core 94, it may abut the inner wall of the ferrite core 94 and may be made unable to move. In this state, input operation with the input pen 90 is impossible. Consequently, it is difficult to reduce the diameter of the lead 92.
On the other hand, since the ferrite core 94 has a through hole in which the lead 92 is inserted, the through hole and the peripheral wall must be reduced in diameter in order to permit the ferrite core 94 to also be reduced in diameter. In addition to the difficulty in reducing the diameter of the lead 92, since ferrite is a fragile structural material, if the ferrite core 94 is excessively reduced, cracking may occur due to insufficient strength.
For example, in the step of winding the coil 95 on the ferrite core 94 in the production process of the input pen 90, tension of the wire is applied to the ferrite core 94. Furthermore, while such winding is performed in a state in which the ferrite core 94 is fixed, stress concentrates on the fixed portion of the ferrite core 94 due to the tension of the wire. Therefore, the ferrite core 94 must correspondingly have great strength. In consideration of vibrations during transportation and dropping shock tests for products, the strength which the ferrite core 94 should have is significantly great.
If the ferrite core 94 is cracked, the inductance of the coil 95 is lowered below its initial value, and the tuning frequency of the tuning circuit 99 is offset. For this reason, the input pen 90 may not work as the input device.
Therefore, the lead 92 and the ferrite core 94 in the input pen 90 must have a predetermined large strength, and it is difficult to reduce the size of the input pen 90 without changing the structure thereof.
Size reduction of electronic devices improves portability, but may decrease ease of input operation. For this reason, there has been a demand for a small input device that provides high operability.
Accordingly, an object of the present invention is to provide a thinner pen-shaped coordinate pointing device which indicates a position to be determined and an operation by an operator to a position detecting device, such as a tablet, for determining the position.
Another object of the present invention is to ensure high operability of a thin pen-shaped coordinate pointing device.
In order to overcome the above problems, according to an aspect of the present invention, there is provided a pen-shaped coordinate pointing device for indicating a position to be determined and an operation by an operator to a position detecting device for determining the position, the pen-shaped coordinate pointing device including: a coil wound on a core having an end face with no opening; and a magnetic member placed along the axis of the coil so as to be opposed to the end face of the core, wherein the core and the magnetic member are spaced from each other and are moved closer together in response to operation by the operator.
For example, the position detecting device has a plurality of loop coils in a flat casing, and it emits radio waves of a predetermined oscillation frequency from the loop coils and detects the position of the pen-shaped coordinate pointing device based on the voltage induced by the radio waves from the coil of the pen-shaped coordinate pointing device. The position detecting device may be formed integrally with a display screen, such as a liquid crystal display panel, and the shape thereof is not limited to a flat shape. The magnetic member is made of, for example, soft ferrite. The core is made of a magnetic member, such as soft ferrite, or of other metals.
In the pen-shaped coordinate pointing device, since the end face of the core does not have any opening, even when the magnetic member and the core are moved closer together, the magnetic member will not enter the interior of the coil.
Accordingly, the inductance of the coil is changed by the movement of the magnetic member closer to the core of the coil, and operation by the operator can be thereby indicated to the position detecting device for determining the position.
Since there is no need to form an opening on the end face of the core, even when the core is reduced in diameter, problems, such as insufficient strength, will not arise. Accordingly, a substantially thin pen-shaped coordinate pointing device can be achieved by reducing the diameter of and placing the core and the magnetic member along the axis of the coil.
Since the core and the magnetic member are moved closer together during operation by the operator, the inductance of the coil increases. A coordinate pointing device used in combination with a position detecting device sometimes has an LC resonance circuit using a variable capacitor, whose capacity changes with pressure in order to detect the operation. In such a coordinate pointing device, when operation is performed by the operator, the capacity of the variable capacitor increases, and, as a result, the resonance frequency of the LC resonance circuit shifts to a lower value. That is, the coordinate pointing device is highly sensitive, whereas it is complicated in structure and is expensive. In the pen-shaped coordinate pointing device of the present invention, since the inductance of the coil increases during operation, the resonance frequency is shifted to a lower value during operation by constructing an LC resonance circuit including the coil. Consequently, a pen-shaped coordinate pointing device, which performs operationally similar to that of the coordinate pointing device using the variable capacitor, can be achieved with a simpler structure and at lower cost.
The change in inductance of the coil during operation is more noticeable as the distance between the coil and the magnetic member decreases. For this reason, operation can be detected more reliably and a smaller pen-shaped coordinate pointing device can be achieved by decreasing the fixed distance between the coil and the magnetic member in an initial state.
Preferably, the pen-shaped coordinate pointing device further includes an elastic member interposed between the end face of the core and the magnetic member.
The elastic member is made of, for example, rubber or flexible resin. The elastic member is formed of, for example, an annular or flat member, a platelike member that partly varies in thickness, or a spherical member.
The elastic member is interposed between the end face of the core and the magnetic member, so that the core and the magnetic member are held with a space therebetween in an initial state before operation. When the core and the magnetic core are moved closer together by operation, they are urged in such a direction as to move apart from each other, and they are returned to the initial state after operation.
Since the return operation is thereby smoothly performed after operation, operability of the pen-shaped coordinate pointing device is improved. That is, high responsivity during operation and a smooth returning mechanism can be provided with a simple structure. The size is easily reduced and the cost is also reduced. Since the amount of deformation of the elastic member due to the force applied thereto generally corresponds to the amount of the force, it is possible to find the amount of deformation of the elastic member based on the amount of change in inductance of the coil and to find thereby the amount of force applied in the operation.
Preferably, the elastic member is in contact with only a part of the end face of the core and is in contact with only a part of a face of the magnetic member opposing the end face of the core, and a part of the end face of the core and a part of the opposing face of the magnetic member are opposed to each other without the elastic member therebetween.
In this case, the elastic member is formed of, for example, a flat plate having a through hole or an annular or spherical member. The elastic member is in contact with only a part of the end face of the core and is in contact with only a part of a face of the magnetic member opposing the end face of the core. That is, the elastic member does not cover the entire end face of the core and the entire opposing face of the magnetic member. A part of the end face of the core and a part of the opposing face of the magnetic member are opposed to each other without the elastic member therebetween. In these parts, magnetic interaction between the core and the magnetic member will not be impeded by the elastic member.
Therefore, the inductance of the coil more noticeably changes during operation in this case than in a case in which the end face of the core or the opposing face of the magnetic member is entirely covered with the elastic member. When a force greater than the elastic force of the elastic member is applied during operation, the core and the magnetic member are moved considerably closer together or are put into contact with each other, which further increases the inductance of the coil.
Since the operation by the operator is thereby detected sensitively and reliably, operability of the pen-shaped coordinate pointing device is improved.
Preferably, at least one of the end face of the core and the face of the magnetic member opposing the end face of the core has a projection having a height less than the thickness of the elastic member.
In this case, a projection and a face or projections are opposed to each other in a portion where the core and the magnetic member are opposed. In other words, the core and the magnetic member are placed closer to each other in an initial state than in a case in which no projection is formed, and they are moved further closer together during operation. Since the height of the projection is smaller than the thickness of the elastic member, the core and the magnetic member are not in contact with each other in the initial state.
The influence of the magnetic member on the inductance of the coil is inversely proportional to the square of the distance between the coil and the magnetic member. Therefore, the inductance of the coil changes more rapidly during operation as the distance therebetween decreases.
Since the projection is provided in the pen-shaped coordinate pointing device of the present invention, it is possible to reduce the distance between the elastic member and the core in the initial state and to quickly move the core and the magnetic member closer to each other during operation. Furthermore, since the height of the projection is smaller than the thickness of the elastic member, the core and the magnetic member can be spaced in a non-operation state only by placing the elastic member therebetween. This prevents the structure from being complicated.
Since the inductance of the coil changes during operation and operation by the operator can be reliably detected by the position detecting device, responsivity and operability can be improved.
Preferably, the elastic member is an annular member having a through hole connected to the end face of the core and the opposing face of the magnetic member, and the projection projects into the through hole of the elastic member.
In this case, when the core and the magnetic member are moved closer together by operation, the annular elastic member is deformed, and the projection projecting into the through hole of the elastic member is moved closer to the opposing face or projection.
When the pen-shaped coordinate pointing device is operated, the annular elastic member is pressed and deformed so as to project in the horizontal direction, and is deformed by a relatively small force. Therefore, the core and the magnetic core can be easily moved close together by small force. This allows the pen-shaped coordinate pointing device to be easily operated by a relatively small force with little resistance.
Preferably, the elastic member is an annular member in linear contact with the end face of the core and the opposing face of the magnetic member, the projection has a side face formed along the inner side face of the elastic member, and both the magnetic member and the core are cylindrical.
In this case, the elastic member is formed of an annular member, such as an O-ring, in linear contact with the core and the magnetic member, and is easily and elastically deformed when the core and the magnetic member are moved closer together. The projection has a side face formed along the inner side face of the elastic member and projects into the space in the center of the elastic member. The elastic member is supported by the contact between the inner side face of the elastic member and the side face of the projection. Both the core and the magnetic member are cylindrical.
Since the elastic member is reliably deformed even by a small force so that the core and the magnetic member are moved close together, the pen-shaped coordinate pointing device can be operated with small resistance during operation by a relatively small force. Since the projection supports the elastic member, the relative position among the core, the magnetic member, and the elastic member can be prevented from being displaced during operation, and reliability of the pen-shaped coordinate pointing device is improved. Furthermore, since the core and the magnetic member are placed along the axis of the core, easy positioning is possible when placing the elastic member between the core and the magnetic member.
Preferably, the core and the magnetic member are held in a pen-shaped casing, a lead is disposed at the leading end of the casing so as to be movably insertable into the casing, and the magnetic member is connected to the base end of the lead.
In this case, when the lead is pushed into the casing by operation of the operator, the magnetic member moves close to the core together with the lead, thereby changing the inductance of the coil.
Therefore, the magnetic member is reliably moved close to the core in response to operation of the operator even in a situation in which it is difficult to transmit the force of operation, for example, when the operator operates the pen-shaped coordinate pointing device while tilting the casing. This ensures reliable response to the operation by the operator and improves operability.
Since the magnetic member is disposed outside the lead, there is no need to form a space or the like for holding the magnetic member inside the lead, and this allows the lead to be reduced in diameter. That is, if a space is formed inside the lead so as to hold the magnetic member therein, the wall portion around the space is thin-walled. Therefore, the lead must not be reduced in order to ensure a strength sufficient for use. Since the lead does not have a magnetic member therein in the pen-shaped coordinate pointing device of the present invention, insufficient strength will not be caused even when the lead is reduced. For this reason, the pen-shaped coordinate pointing device can be reduced by reducing the diameter of the lead. When the lead is reduced, only a small hole is needed at the leading end of the casing for passing the lead therethrough, and therefore, the casing can be reduced easily. Moreover, when the lead serving as the pen point is reduced, efficiency in fine operation is enhanced. For example, the casing can be substantially reduced by arranging the lead, the magnetic member, the elastic member, and the core in series along the axis of the core. This can further reduce the diameter of the pen-shaped coordinate pointing device.
Further objects, features, and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.